Why I can't use GetOwner()->?

I use the ue4.16.3 and vs2017.
Then i writed the code GetOwner()->,but the IDE told me that “pointer to imcomplete class type is not allowed”

And the same code in mac xcode is fine. no error.
Who can tell me ?

Finally,the solution is “#include 'ProjectName’GameModeBase.h” in your *.h file which you want to type GetOwner()->